The present invention relates to fluid actuators, and particularly to pneumatic or hydraulic actuators.
Fluid actuators are now widely used for controlling valves, such as butterfly valves or ball valves having angularly-movable value operators. Most of these valves are usually of the pneumatic type driven by compressed air, although some are of the hydraulic type driven by a hydraulic liquid, such as oil. Usually, the valve operator is driven about 90.degree. from its open to its closed positions.
Probably the most popular fluid actuator presently used is the cylinder-type wherein the driving fluid reciprocates a piston, the actuator including means for converting the piston reciprocations into angular movements of an output shaft. Such actuators, however, are complicated and expensive in construction.
Another actuator now in use is of the vane type, wherein the driving fluid acts directly on a rotating vane rigidly coupled to the output shaft. This type, as well as the first-mentioned type, requires high quality internal surfaces to decrease friction, which requirement increases the manufacturing costs substantially.
A further actuator now in use is the diaphragm-type wherein the driving fluid reciprocates a diaphragm, the reciprocations of the diaphragm being converted into angular movements of an output shaft. The known actuators for this type, however, require bulky constructions.
An object of the present invention is to provide a new type of fluid actuator having advantages in the above respects.